1. Field of the Invention
The present invention is directed to a new capillary viscometer for measuring the flow properties, especially viscosity, of liquids, such as engine oil, at high temperatures and high shear rates.
2. Description of the Prior Art
Many types of viscometers have been used for the measurement of flow properties of liquids. These include:
a. Capillary viscometers; and PA1 b. Rotational viscometers.
Capillary viscometers include glass capillary kinematic viscometers (see ASTM specifications D446 and U.S. Pat. No. 2,805,570) which operate with a liquid flow induced by gravity and produce relatively low shear rates. Other capillary viscometers utilize vacuum or pressure to cause liquid flow (see ASTM test method D2171 and U.S. Pat. No. 3,277,694) and produce higher shear rates.
These capillary viscometers are not designed for high-temperature, high-shear operation. Thus, they are unsuitable for viscosity measurements at high-temperature ahd high-shear, as described herein.
U.S. Pat. Nos. 3,435,665 and 4,441,358 disclose capillary viscometers. U.S. Pat. No. 3,435,665 discloses a capillary tube directly connected to an manometer. An inert fluid forces a test fluid through the capillary tube. The moving test fluid causes the manometer fluid to fluctuate within the manometer tube. Two photoelectric cells are operatively connected to a timer. The photoelectric cells and timer measure the lapse time it takes the meniscus of the manometer fluid to travel between two points on the manometer tube. This capillary viscometer is not adapted for high-temperature, high-shear viscosity measurements. U.S. Pat. No. 4,441,358 discloses a capillary viscometer having at least two sets of piezo electric ultrasonic transducers mounted along a length of the capillary tube. The transducers monitor the movement of the test fluid meniscus as it travels between the transducers. The transducers initiate and terminate the timer. This viscometer does not disclose the present invention.
Rotational viscometers include the Stormer Viscometer which is used to produce low shear rates. The Kingsbury Tapered-Plug Viscometer (see ASTM Special Technical Bulletin No. 111 (1951), S. J. Weeds, "The Kingsbury Tapered-Plug Viscometer For Determining Viscosity Variations Within Temperature and Rates of Shear") and the Tapered Bearing Simulator (U.S. Pat. No. 4,274,279) are suitable for the measurement of engine oil lubricant flow properties at high temperatures (100.degree. to 200.degree. C.) and at high shear rates of 10.sup.6 sec.sup.-1. These two high shear rotational viscometers are well suited for laboratory research purposes, but are complex in operation and require highly trained technicians and maintenance personnel for operation and repair.
There is a need for a relatively simple viscometer which overcomes the complexity of the tapered-rotational and rotational instruments, which has the relative simplicity of capillary viscometers, and that can be adapted to high-temperature high-shear operation.